Java ME recall screen problem

I'm having trouble recalling a screen. I'm building a small BMI app. The idea is you enter your details and submit them, then you get your result and get 2 options... to cancel... or calc, when calc is called it calls the BMIMenu Method again to redraw to opening menu. The method works fine when it draws the opening screen but when i recall the method after calculating the BMI I get an error... can anyone help me. Thanks

This Method seems to be the main problem. If i delete form.append(height); and form.append(weight); then the program will work but i need those textboxes